Several prior art spine fixation assemblies utilize rods and/or plates as connecting and stabilization elements between vertebral elements. The rods are secured to vertebral bones left and right the spinal midline via screws. The screws in some of the prior art assemblies are capable of pivoting around a fixed axis of the stabilization rods to achieve variable angular positions relative to the rods. This limited range of relative angular positioning is acceptable for many spinal pathologies. However, in some cases it is preferred to have screws that provide multi-axial positioning relative to the stabilization rods.
Single or multilevel segmental posterior fusions are most commonly achieved by contouring a rigid ¼ inch cylindrical rod and attaching it to adjacent pedicle screws on each side of the spine using various connecting assemblies. This longitudinal construction can be made more rigid by connecting the rods to each other to form an “H” configuration. The rod system requires contouring of each rod across several vertebras in many cases. The contouring of each rod depends on the configuration of the pedicle screws and varies from side to side in the same patient and among patients. This may add considerable time to an operation. Recent generations of pedicle screws and rod connectors seek to diminish this drawback by allowing variable axes of movements in the pedicle screw recess for the rod or in the rod connectors. However, in most cases this adds another level of complexity to the operation and often further increases the operative time. This increase in operative time and the complexity of the connectors put substantial stress on the surgeon and the supporting staff. Even in the hands of the best spine surgeon, the rod is often not perfectly contoured to align with the pedicle screws. Hence the surgeon has to use substantial force at multiple points along a rod to hold the rod to the screws or connectors while counteracting the adjacent soft tissues. This maneuver risks soft tissue damage and also puts the dura and the neural contents at risk for dural tears or spinal cord or nerve damage if a holding instrument slips.
Accordingly, there is a need for an improved spinal fixation device and method that does not require rod contouring and allows multi-axial screw anchoring.